Auto exclusions has a regression in 4.3-dev

[jngrad]

A regression was introduced in 4.3-dev by 5add7f8 from #4541. The auto-exclusion feature no longer runs in parallel due to a missing MPI guard in the script interface System class:

$ mpiexec -n 2 ./pypresso testsuite/python/auto_exclusions.py
terminate called after throwing an instance of 'std::logic_error'
  what():  Callbacks can only be invoked on rank 0.

The following patch fixes the regression:

diff --git a/src/script_interface/system/System.cpp b/src/script_interface/system/System.cpp
index aaa3ca554..62f743396 100644
--- a/src/script_interface/system/System.cpp
+++ b/src/script_interface/system/System.cpp
@@ -82,6 +82,8 @@ Variant System::do_call_method(std::string const &name,
 #ifdef EXCLUSIONS
   if (name == "auto_exclusions") {
-    auto const distance = get_value<int>(parameters, "distance");
-    auto_exclusions(distance);
+    if (context()->is_head_node()) {
+      auto const distance = get_value<int>(parameters, "distance");
+      auto_exclusions(distance);
+    }
     return {};
   }

This regression was not caught by the testsuite, because auto_exclusions.py doesn't run in parallel.